The main objectives of the program are to provide an insight into the genetic organization of the H-2 complex, to elucidate the involvement of different H-2 regions in various phenomena of cellular immunity, to obtain some notion of the functional interrelationship of the individual H-2 regions, and, finally, to seek out clues to the evolutionary significance of the H-2 system. The specific goals of the project include the following: to complete development of two new H-2 recombinant strains; to determine the role of H-2 regions in heart transplantation; to analyze by skin grafting H-2 recombinants B10.S(7R), B10.S(9R), B10.HTT, and some others; to analyze the A.CA(M506) mutant serologically and genetically and to determine the role of the H-2fa mutation in MLR and CML; to determine the molecular relationships of the serologically detectable new mutant antigens H-2da and H-2fa; to develop a radioimmuno assay for Ss and Slp determination and to use the assay for genetic H-2 mapping.